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A Genetic Analysis of Sow Productivity Traits

US Department of Agriculture³, Beltsville, MD 20705

Abstract

Genetic and phenotypic parameters for sow productivity traits were derived from analyses of records for 999 purebred Duroc and Yorkshire litters at the Beltsville Agricultural Research Center. Included were 682 spring-farrowed litters and 317 fall-farrowed litters. Primary traits examined were number of pigs born alive in the litter (N_A), litter size at 21 d of age (N₂₁), litter weight at 21 d (W₂₁) and an index (I₂₁) combining the three traits. Also analyzed were total number of pigs farrowed alive or stillborn, litter weight of pigs born alive and litter size and litter weight at 42 d of age (weaning). Selection was based mainly on the sow productivity index among litters in the spring season and mainly on performance traits among fall-farrowed pigs. Select and control lines were maintained in both breeds in both seasons. Yorkshires started at higher levels of productivity than Durocs in spring 1975, showed more fluctuation and ended in spring 1982 at about their starting levels. Durocs started at lower productivity levels and recorded generally significant increases by 1982, with comparable selection differentials for the two breeds. Heritabilities, estimated from daughter-biparental (mid-dam, paternal granddam) regressions using records expressed as deviations from contemporary breed-line means, varied widely among the breed-line groups. Suggested composite heritability estimates were 5, 10 and 20% for N_A N₂₁ and W₂₁, respectively. Genetic correlations, computed from daughter-biparen-tal covariances, were high and positive (.7 or above) among all traits. Based on estimated genetic gains, it was proposed that W₂₁, alone or in combination with N₂₁ and(or) N_A in an index, be used as the primary selection criterion to bring about genetic improvement in sow productivity traits.

¹ USDA, Agricultural Research Service, Beltsville Agricultural Research Center, Animal Science Institute, Nonruminant Animal Nutrition Laboratory, Beltsville, MD 20705.

² The author acknowledges with appreciation the contributions of R. L. Figulski and D. L. Parsons, Animal Caretaker Leaders, for managing the swine herd and for collecting and recording the necessary data; the cooperation of W. H. Peters, Supervisory Animal Husbandman; and the contributions of Bonnie Morgan, Statistical Assistant.

³ Mention of the trade name, proprietary product or vendor does not constitute a guarantee or warranty of the product by the USDA and does not imply its approval to the exclusion of other products or vendors that may also be suitable.